Structural rehabilitation renovation and restoration of existing structures
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n 2009, maintenance workers at Canada Place observed brown spots on several stay cables of its large fabric membrane roof. Based on this observation, Canada Place Corporation, the authority for maintaining the facility, launched an evaluation of the cables and the protective coating of the wires that make up the cables. Wires that make up the cables are protected against corrosion as they generally are used at high-stress levels. Corrosion of the wires causes surface discontinuities that can result in stress risers and reduce the load capacity of the wires and, thus, the cable.
the roof. The stay cables are anchored along the edge of the promenade and cross over it to the top of the masts (Figure 2). The stay and ridge cables are 27/8-inch diameter wire strands and are comprised of one hundred ¼-inch diameter wires. The ridge cables are positioned external to the fabric and thus are exposed to the environment. Stainless steel loops wrap over the cables and are bolted to a clamp system that holds the fabric (Figure 3). Due to the proximity to the salty sea water of the bay, a Class C coating (see below) was specified for all cables.
Canada Place
Wires for cables are fabricated from high-strength steel that are rolled to a circular or Z-shaped section and then drawn through a mandrel to their final size. The cold working of the steel during this process increases the strength of the wires. A protective coating is applied after the cold working process. There are several corrosion-resistant systems for cables. The most common one is a process of coating its wires. Various protective wire coatings include epoxy, zinc-aluminum-mischmetal, and pure zinc coatings, though the zinc coating is by far the most common one. Three levels of zinc protection are listed in the American Society for Testing and Materials ASTM A475-03 (Standard Specification For Zinc-Coated Steel Wire Strand) and ASTM A603 (Standard Specification For ZincCoated Structural Wire Rope), the specifications for strand and rope cables. Class A is the most widely used and sufficient for the most common applications. Class B is used
Canada Place was built in 1986 in Vancouver, British Columbia. It houses a hotel and convention center that also serves as the terminal for cruise ships that frequently dock in Vancouver’s harbor. It is owned and operated by the Vancouver Fraser Port Authority, which is responsible for the stewardship of federal port lands in and around Vancouver. The main feature of the building is a large tent-like fabric membrane structure that covers most of the convention center space (Figure 1). The roof spans 170 feet and is 478 feet long. Its system of cable-stayed masts are spaced 80 feet apart and are 125 feet high. The masts anchor the ridge cables that support the membrane roof and are located along promenades at each side of
Repair of Corrosion Protection for Cables A Case Study By Paul A. Gossen, P.E., F.ASCE
Paul A. Gossen is a Member of the ASCE Committee 19 – Structural Application of Steel Cables for Buildings, as well as the ASCE Committee 55 –Tension Membrane Structures Standards Committee. He can be reached at pag@geigerengineers.com.
Figure 1. Canada Place.
24 July 2016
Cable Fabrication and Protection
